We propose to use promoter-regulated ribozymes delivered by recombinant virus vectors developed in our laboratories as a genetic challenge to the retina of experimental animals. Specifically, we will profile the expression response of photoreceptors to having key individual phototransduction mRNAs down regulated in an otherwise normal rodent retina. Riboenzymes are RNA enzymes that have the potential to block the expression of specific genes. In the past, we have successfully used Adeno-associated virus (AAV) to deliver ribozymes as therapy in rodent models of dominant genetic diseases of the retina. Our plan will employ the analogous approach, this time delivering ribozymes against wild type gene sequences, to create retinas altered initially in a single normal photoreceptor mRNA, and then to profile the expression response globally using photoreceptor gene-specific array technology. This technique permits the generation of in vivo somatic gene knock- outs, avoiding problems commonly associated with transgenic or germ line knock-out animals, including embryonic lethality, experimental inaccessibility due to early developmental expression, and a practical problem limiting most transgenics to genes of known function or disease etiology. Our two-year goal will be to validate the AAV-ribozyme approach by following the expression response of rod photoreceptors to altered levels of mRNAs for either of two well-studied phototransduction genes, the beta- or gamma-subunits of rod cGMP- phosphodiesterase (PDE). Expression patterns will be compared with those from both control retina in the same animal and from retina in mice with endogenously altered levels of beta- or gamma-PDE mRNA in order to determine whether ribozymes against a given mRNA cause the same global expression changes as genetically determined changes. Finally, the temporal pattern of expression profile changes will be determined in order to distinguish initial cellular responses from more downstream events such as activation of apoptotic pathways. The generality of this strategy needs to be emphasized. Even in this feasibility study, we are likely to uncover new gene functions in rods, identify new candidate genes for retinal disease and, more generally, perfect an in vivo expression profiling technology of wide utility in a variety of tissues throughout the body.